This invention generally relates to a vehicle hydraulic brake apparatus. More particularly, the invention pertains to a brake stroke simulator for a vehicle hydraulic brake apparatus that provides operational feeling of a brake pedal to a driver.
An example of a brake stroke simulator is disclosed in Japanese Patent Laid-Open Publication No, 3(1991)-45456. This brake stroke simulator is applicable to a hydraulic boosting apparatus for hydraulically boosting a master cylinder. An accumulator defined in the brake stroke simulator is in communication with a reaction force chamber defined in a brake booster. The volume of the reaction force chamber is decreased in response to an increase in the output, i.e. an increase of the depressing force applied to the brake pedal.
The brake stroke simulator is provided with a first piston and plural second pistons in a cylindrically shaped main body. The first piston is freely slidably disposed in the main body and defines the accumulator between one end of the first piston and one end wall of the main body. The plural second pistons are disposed at an opposite side of the accumulator relative to the first piston and are disposed in the main body for sliding movement at a predetermined stroke. Springs and shock absorbing rubber elements are disposed between the adjacent second pistons and between the second piston and the other end wall of the main body. The number of springs and shock absorbing rubber elements corresponds to the number of second pistons disposed in the brake stroke simulator. Each spring has a different spring constant and applies a biasing force to each corresponding second piston for biasing the second piston towards the first piston. Each shock absorbing rubber element is designed to be elastically compressed by each corresponding second piston when the second piston is displaced at the predetermined stroke in an opposite direction to the first piston.
With this construction of the brake stroke simulator, the first piston is displaced towards the second piston corresponding to the fluid amount supplied to the accumulator from the reaction force chamber in response to the depressing operation of the brake pedal. The displacement of the first piston urges the plural second pistons to be sequentially displaced so as to compress the plural springs in ascending order of the spring constant. The shock absorbing rubber elements are elastically compressed while the springs have been compressed in the ascending order of their spring constants. Although the springs are sequentially compressed as described above, the total spring characteristics exerted for smoothly increasing the reaction force against an increase of the displacing amount of the first piston is represented not by a sequential line, but by a quadratic curve. Therefore, the reaction force is transmitted to the reaction force chamber via the fluid and is applied for providing a good brake operational feeling to the driver.
However, the disclosed brake stroke simulator is provided with the same number of shock absorbing rubber elements as the number of the springs. In such a case, the number of the components included in the brake stroke simulator is relatively large, thus making it difficult to reduce the manufacturing cost of the brake stroke simulator, as well as the size and weight of the brake stroke simulator.
Accordingly, the above disclosed brake stroke simulator is still susceptible of certain improvements with respect to providing a good brake operational feeling to the driver while at the same time reducing the number of components required for the brake stroke simulator.
A brake stroke simulator for supplying a brake stroke corresponding to an operational force applied to a brake operating member includes a housing, a first movable member, a second movable member, a first spring, a second spring, and a shock absorbing elastic member. The first movable member is freely slidably disposed in the housing in a fluid-tight manner and defines a hydraulic pressure chamber supplied with hydraulic pressure corresponding to the operational force applied to the brake operating member at one end side of the first movable member. The second movable member is disposed at the other end of the first movable member in the housing and is movable integrally with the first movable member in response to sliding movement of the first movable member in a direction for increasing a volume of the hydraulic pressure chamber. The first spring biases the first movable member in a direction for reducing the volume of the hydraulic pressure chamber while the second spring biases the second movable member in the same direction as the biasing direction of the first spring, with the first and second springs having different spring constants. The shock absorbing elastic member is compressed by the first movable member upon sliding movement of the first movable member at a predetermined stroke against the biasing force of the first spring and is compressed by the second movable member upon sliding movement of the second movable member at a predetermined stroke against the biasing force of the second piston.
According to another aspect, a brake stroke simulator for supplying a brake stroke corresponding to an operational force applied to a brake operating member includes a housing, a slidably movable simulator piston disposed in the housing in a fluid-tight manner and defining a hydraulic pressure chamber in the housing at one side of the simulator piston which is adapted to receive hydraulic pressure corresponding to the operational force applied to the brake operating member, a movable elastic member holder disposed in the housing at an opposite side of the simulator piston, a first spring biasing the simulator piston in a direction for reducing the volume of the hydraulic pressure chamber, and a second spring biasing the elastic member holder in the same direction, with the first and second springs having different spring constants. A compressible elastic member is held on the elastic member holder and is compressible by the simulator piston upon sliding movement of the simulator piston against the biasing force of the first spring.
Another aspect involves a vehicle hydraulic brake apparatus provided with a stroke simulator. The vehicle hydraulic brake apparatus includes a wheel cylinder operatively mounted on a vehicle wheel for applying a brake force to the vehicle wheel, a master cylinder operatively connected to a brake pedal for generating master cylinder hydraulic pressure in response to an operational force applied to the brake pedal, a hydraulic pressure generating device different from the master cylinder, a hydraulic pressure control valve disposed between the hydraulic pressure generating device and the wheel cylinder for adjusting brake hydraulic pressure of the wheel cylinder by applying hydraulic pressure outputted from the hydraulic pressure generating device, a first opening and closing valve for selectively connecting and disconnecting the master cylinder and the wheel cylinder, with the brake stroke simulator being operatively connected to the master cylinder to provide a brake pedal operational feeling with the first opening and closing valve under a closed condition, a second opening and closing valve for selectively connecting and disconnecting the master cylinder and the brake stroke simulator, a brake operating amount detecting means for detecting an operational amount of the brake pedal, and control means for closing the first opening and closing valve and opening the second opening and closing valve during operation of the hydraulic pressure generating device, and for controlling the hydraulic pressure control valve in response to an output detected by the brake operating amount detecting means. The brake stroke simulator includes a housing, a first movable member, a second movable member, a first spring, a second spring, and a shock absorbing elastic member. The first movable member is freely slidably disposed in the housing in a fluid-tight manner and defines a hydraulic pressure chamber supplied with hydraulic pressure corresponding to the operational force applied to the brake operating member at one end side of the first movable member. The second movable member is disposed at the other end of the first movable member in the housing and is movable integrally with the first movable member in response to sliding movement of the first movable member in a direction for increasing a volume of the hydraulic pressure chamber. The first spring biases the first movable member in a direction for reducing the volume of the hydraulic pressure chamber while the second spring biases the second movable member in the same direction as the biasing direction of the first spring, with the first and second springs having different spring constants. The shock absorbing elastic member is compressed by the first movable member upon sliding movement of the first movable member at a predetermined stroke against the biasing force of the first spring and is compressed by the second movable member upon sliding movement of the second movable member at a predetermined stroke against the biasing force of the second piston.